A series of lanthanoid trigermanides of Pr, Nd, and Tm has been prepared by high-pressure (35 GPa) and hightemperature (1200°C) reactions. TmGe 3 crystallizes in an orthorhombic unit cell (Cmcm, No. 63) with a = 3.990(1) ¡, b = 20.488(5) ¡, c = 3.8794(8) ¡, and V = 317.2(1) ¡
3. It is isotypic with the DyGe 3 structure composed of Ge zig-zag chains and Tm situated between double square Ge-meshes. PrGe 3.36 crystallizes in an orthorhombic unit cell (Cmmm, No. 65) with a = 4.062(4) ¡, b = 21.43(3) ¡, c = 4.212(6) ¡, and V = 366.6(8) ¡ 3 . The structure is principally the same to the DyGe 3 structure but contains an additional Ge site. The site is partially occupied, and is situated on the square mesh. Each Ge atom in the site is coordinated by five Ge atoms in the chain and in the mesh. , Tb 3+ , and Gd 3+ form the DyGe 3 structure. 16 The structure contains two types of Ge subunits as shown in Figure 1.1 One is a zig-zag chain and the other is a layer composed of double square meshes. Dy ions and the Ge chains are situated between the layers. The space group is Cmcm and the double meshes are stacked along the b axis. The chains extend along the c axis corresponding to the diagonal direction of the meshes. The lattice constants of the a (4.0278(5) ¡) and c (3.8997(5) ¡) axes of DyGe 3 are very similar but not the same, because the mesh is slightly distorted from the regular square net.Light lanthanoid elements do not form the DyGe 3 structure. For these elements, only the compounds with compositions of LnGe x with x¯2 have been reported by reactions under ambient pressure. However, in our recent studies, Ge rich compounds were obtained by high-pressure and high-temperature reactions, such as LnGe 5 , Ln = La, Ce, Pr, Nd, and Sm with the LaGe 5 structure, and CeGe 3 with the Cu 3 Au structure. 79 The former has a tunnel structure composed of GeGe covalent network containing uncommon 8-coordinated Ge atoms.We are interested in the structures of Ge networks in lanthanoid germanides formed under high pressure. In the present study, we have investigated the reactions of Pr, Nd, and Tm with Ge and successfully prepared three new germanides PrGe 3.36 , NdGe 3.25 , and TmGe 3 with the aid of high-pressure and high-temperature conditions. They have the DyGe 3 structure (for Tm), and its closely related structures (for Pr and Nd).
ExperimentalThe new lanthanoid germanides were prepared as follows: Pr (Nilaco 99.9%) and Tm (Nilaco 99.7%) were reacted with Ge (Mitsuwa Pure Chemical 99.999%) in a molar ratio of 1:3 in an arc Figure 1. The crystal structure of DyGe 3 . The yellow and green balls represent Dy and Ge atoms, respectively. It has a layer structure composed of Dy 3+ ions, double square Ge-meshes, and Ge-chains.